The present invention relates to data networking, and in certain embodiments to clock recovery in data networking applications.
As service provider optical transport networks grow and evolve to incorporate more advanced technologies, they increasingly make use of multiple types of optical signal, rather than just one that is standardized across the network. The various optical transmission standards include synchronous transmission standards where the various network nodes share common transmission timing and asynchronous transmission standards where each node transmits in accordance with its own clock. Synchronous transmission standards include, e.g., SDH, SONET, etc. Asynchronous transmission standards include e.g., 1 Gigabit Ethernet, 10 Gigabit Ethernet, etc.
The network manager thus confronts a wide variety of optical transmission standards, and consequently a wide variety of optical transponders that are responsible for transmitting and receiving the optical signals. Unfortunately, given the inherent compatibility differences between transmission standards, a transponder of one type can only be used with signals of that type. The result is great inflexibility in network configuration. Transponders specified for one signal type can only be used with that signal type and not with other signal types.
A need thus arises for employing a single transponder that can send and receive using multiple optical transmission standards. A problem, however, arises in using a single design of transponder and associated circuitry with both synchronous and asynchronous transmission standards. Such a transponder may be found on a line-card of a network device. On what is referred to as the “trunk side,” the transponder has an optical interface to couple to an optical transmission medium. On what is referred to as the “client side,” the transponder interfaces to a backplane connector of the network device. Data received from the backplane connector is sent out over the optical interface and vice versa.
The interface to the backplane is a high-speed electrical interface and it is desirable to use commercially available integrated circuits. Such integrated circuits have been developed for use with the 10 Gigabit Ethernet transmission standard. These parts, referred to as “transceivers,” assume an asynchronous timing architecture. Both directions of data output by the transceiver are clocked by a local reference clock source.
It would be desirable to use an asynchronous data transmission standard transceiver to also carry data which is carried in accordance with a synchronous transmission standard on the trunk side. However, it is not appropriate to clock SONET or SDH transmissions using a locally generated clock source. Instead, the timing for these transmissions is determined based on a clock that has been recovered from a received signal. What is needed are systems and methods for employing asynchronous transmission standard transceivers to support participation in synchronous communications.